I've had both units and I like the SAFC II since it's smaller and I like the displays a lot more. The II has a knock sensor montior plus a higher resolution fuel correction map (the old one had 500rpm increments, the new one has 200rpm.)
Previous S-AFC
*Air correction factor setting point - Option 8 point option
*Air revision engine rpm setting - 500rpm to cut
New SAFC II
*Air correction factor setting point - Option 12 point
*Air revision engine rpm setting - 200rpm to cut
*Drive voltage stabilization of circuit precision - improvement of air flow signal
*Monitor indication optimization - designated item (air flow * pressure) indication
*Knocking level Monitor
*New monitor picture (digital analyzer indication)
*Setting data of 2 patterns memory (you can have 2 settings saved plus one running)
*Correction bypass function
*Warning function
*Password lock function
